The invention concerns spectrophotometry, i.e. the study of optical transmission properties of substances.
Among the known applications of spectrophotometry, the study of biological media (capable of photosynthesis) which strongly diffuse light, is a particularly delicate one. Its progress is limited by the analysis apparatus available to the experimenter, and more particularly by the spectrophotometers, as is indicated in the following publications:
"Une nouvelle methode spectrophotometrique destinee a l'etude des reactions photosynthetiques", Pierre Joliot, Daniel Beal and Bernard Frilley; Journal de Chimie Physique, 1980, 77, No. 3.
"Electron Transfer between the two photosystems, I. Flash Excitation under oxidizing conditions", Pierre Joliot and Anne Joliot, Biochimica et Biophysica Acta, 765 (1984) 210-219 Elsevier.
In most high performance applications, the spectrophotometers operate in a differential mode. This means that the measurement of the optical transmission coefficient is done simultaneously on a measurement sample and on a reference sample. More generally, it is conceivable to produce a differential measure between two working samples which undergo different conditions. It is therefore known to use a differential spectrophotometer which includes a monochromatic measuring light source, more especially in the form of monochromatic flashes of short duration, an optical feeder to apply this light to both samples at the same time, as well as two photodetectors to selectively receive the light transmitted through each one of the two samples, during the operation of the measuring light source in order to compare the behavior of these two samples, as described in the abovementioned paper in Journal de Chimie Physique.
The performance of a spectrophotometer is mainly determined by its resolution, which depends upon numerous factors.
The permanent goal of persons skilled in the art is therefore to improve this resolution.
The very particular field of biological studies with respect to photosynthesis is the subject of specific limitations, namely regarding the intensity of the measuring light. This results in differences between this particular application and the other applications of spectrophotometers.
The publication in the Journal de Chimie Physique mentioned above, describes an instrumental technique used for studying the photosynthetic reactions, and includes useful instructions for improving the resolution.